Skill and guts. That’s what it takes to be an ironworker, raising the city’s skyscrapers and bridges from heights that, for most of us, would churn the stomach. Legendary among these steely nerved tradesmen are the Mohawk Indians, who have been performing their narrow beam balancing acts for the past 100 years. At the World Trade Center, generations of Native Americans worked on the original buildings. They were part of the the rescue and recovery effort of 9/11, and they helped to construct the towers that are there today.

In a fitting tribute to those workers, the 9/11 Memorial & Museum has mounted an exhibition of 30 photographs, “Skywalkers: A Portrait of the Mohawk Ironworker at the World Trade Center,” by Melissa Cacciola. It is a show that Alice Greenwald, the museum’s president and CEO, called “a powerful testament to the shared history of the Mohawk ironworkers and the World Trade Center site.”

In 2012 and 2013, Cacciola made portraits of the ironworkers using the tintype process, a laborious medium that dates back to the 1850s and made popular during the Civil War as mementos to send to loved ones. The contrast and subtle tonality of the artist’s pictures evoke early photographic portraiture. There are no smile-quick-for-the-camera expressions here. Cacciola’s subjects, their strong features further enhanced by her choice of lighting, must remain motionless for 10 to 15 seconds, the length of time it takes to expose the silver on the metal plate.

“It’s about photographing someone as they would want to be represented and it’s about trust,” said Cacciola, whose tintype portrait projects have included Afghanistan war vets, New Orleans musicians and skateboarders. “You’re never going to get a good portrait if there’s not some relationship, some element of trust. You’re working together to make something beautiful.”

Cacciola spoke about the project during a recent panel discussion at the museum, moderated by Amy Weinstein, the museum’s vice president of collections and oral history. With her was one of her subjects, Lindsay LeBorgne, a fourth-generation ironworker and Brooklynite with roots in the communities of the Mohawk Nation, which lie along the border of the U.S. and Canada. His father worked on the original World Trade Center. Years later, after 9/11, LeBorgne put in long shifts in the rubble of the site, cutting down and removing the steel, and searching for victims.

As for the long-held belief that Native Americans have a special gift of balance and nerve, LeBorgne said, “You hear a lot of stories like that but I think it’s more a very healthy respect, not a fear so much, but you respect the fact that the wrong step, or doing something you shouldn’t be doing, could either severely injure you, kill you or hurt somebody else.”

In August, 1907, the collapse of a bridge under construction near the Kahnawake Reserve in Canada killed 34 Kahnawake Mohawk ironworkers. The tragedy is said to have led to the migration of Mohawks to the city where there was more work, and no single accident could again yield such devastation to the tribe. “At the time there were only about 600 residents,” LeBorgne said, “so that was a real blow to the community.”

The danger remains part of the job. Bob Walsh, a panel member and the business manager of Local 40, the ironworkers’ union, comes from a five-generation family of ironworkers. His father died on the job when Walsh was 11. His son, he said, was almost killed. And Walsh himself fell from a height of 220 feet—only to be caught by a safety net.

“It’s very hard work, very dangerous, you never know if you’re going to be coming home at night,” Walsh said. “When we get hurt, we really get hurt.”